The present invention relates to methods and systems for performing corrective eye surgery. In particular, the present invention relates to surgical methods and systems providing a laser beam having an energy distribution profile arranged to cause ablation of eye tissue to a generally uniform depth.
Ultraviolet and infrared laser based systems and methods are now used in ophthalmological surgery on the cornea to correct vision defects. These procedures, generally referred to as photorefractive keratectomy, generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea to alter its refractive power. In ultraviolet laser ablation procedures, the radiation ablates corneal tissue in a photodecomposition process that does not cause thermal damage to adjacent and underlying tissue. Molecules at the irradiated surface are broken into smaller volatile fragments without heating the remaining substrate. The mechanism of the ablation is photochemical, i.e., the direct breaking of intermolecular bonds. The ablation removes stromal tissue to change the contour or shape of the cornea for various purposes, such as correcting myopia, hyperopia, and astigmatism. Such systems and methods are disclosed in the following U.S. patents and patent applications, the disclosures of which are hereby incorporated by reference: U.S. Pat. No. 4,665,913 issued May 19, 1987 for xe2x80x9cMethod for Ophthalmological Surgeryxe2x80x9d; U.S. Pat. No. 4,669,466 issued Jun. 2, 1987 for xe2x80x9cMethod and Apparatus for Analysis and Correction of Abnormal Refractive Errors of the Eyexe2x80x9d; U.S. Pat. No. 4,732,148 issued Mar. 22, 1988 for xe2x80x9cMethod for Performing Ophthalmic Laser Surgeryxe2x80x9d; U.S. Pat. No. 4,770,172 issued Sep. 13, 1988 for xe2x80x9cMethod of Laser-Sculpture of the Optically Used Portion of the Corneaxe2x80x9d; U.S. Pat. No. 4,773,414 issued Sep. 27, 1988 for xe2x80x9cMethod of Laser-Sculpture of the Optically Used Portion of the Corneaxe2x80x9d; U.S. patent application Ser. No. 07/109,812 filed Oct. 16, 1987 for xe2x80x9cLaser Surgery Method and Apparatusxe2x80x9d now U.S. Pat. Nos. 5,108,388; 5,163,934 issued Nov. 17, 1992 for xe2x80x9cPhotorefractive Keratectomyxe2x80x9d; U.S. patent application Ser. No. 08/368,799, filed Jan. 4, 1995 for xe2x80x9cMethod and Apparatus for Temporal and Spatial Beam Integrationxe2x80x9d now U.S. Pat. No. 5,646,791; U.S. patent application Ser. No. 08/138,552, filed Oct. 15, 1993 for xe2x80x9cMethod and Apparatus for Combined Cylindrical and Spherical Eye Correctionsxe2x80x9d now U.S. Pat. No. 5,713,892; U.S. patent application Ser. No. 08/058,599, filed May 7, 1993 for xe2x80x9cMethod and System for Laser Treatment of Refractive Errors Using Offset Imagingxe2x80x9d now abandoned; and U.S. patent application Ser. No. 09/303,810, filed Apr. 30, 1999 for xe2x80x9cMethod and System for Ablating Surfaces with Partially Overlapping Craters Having Consistent Curvaturexe2x80x9d.
Refractive surgery often makes use of laser ablation to selectively remove corneal tissues, thereby resculpting the cornea to reduce myopia, hyperopia, astigmatism, or other refractive defects. This resculpting generally directs varying amounts of laser energy across the cornea. The lasers often produce beams comprising a series of laser pulses, and the laser systems generally vary a size, shape, and/or location of these pulses to effect the predetermined resculpting.
The lasers used in laser eye surgery systems often produce beams having Gaussian energy distribution profiles, as measured across a cross-section of the laser beam. These systems often include optical elements (sometimes referred to as integrators) which modify the energy distribution to a more uniform profile. Unfortunately, work in connection with the present invention has found that when a laser beam having a uniform energy distribution profile extending across its cross-sectional area is used to remove or to sculpt eye tissue, a non-uniform ablation depth ensues. Referring to FIG. 1 of the accompanying drawings a laser beam having a uniform energy distribution profile is indicated at 10, the resultant non-uniform ablation depth being indicated at 20. This non-uniform ablation depth reduces the overall accuracy of the resculpting procedure, thereby limiting the benefits of these new systems.
In light of the above, it would be desirable to provide improved devices, systems, and methods for laser eye surgery. It would further be desirable if these improvements did not increase the complexity and cost of the laser system, and made use of laser ablation algorithms or treatment protocols which reflected actual experience in ablations, rather than relying on simplified theoretical ablation depth calculations. It would further be advantageous if these improvements did not prolong the total treatment time and reduced the number of individual ablations which are used to effect a desired resculpting so as to avoid additional ablation edge-induced surface roughness.
According to one aspect of the invention, there is provided a method of performing corrective eye surgery, the method comprising directing a laser beam at a cornea region of an eye of a patient, the laser beam having a cross-sectional area; and adapting an energy distribution profile extending across the cross-sectional area of the laser beam to provide a resultant laser beam having a non-uniform energy distribution profile so as to cause a generally uniform ablation depth when the cross-sectional area of the laser beam is directed at the cornea region of the patient""s eye.
The adapting step can comprise causing the laser beam to have a centrally disposed higher energy region surrounded by a peripheral lower energy region.
The method can further comprise generating the laser beam with a generally Gaussian energy distribution profile extending across its cross-sectional area, the adapting step changing the Gaussian profile to provide the resultant energy distribution profile.
The adapting step can comprise directing the laser beam through a diffractive optic.
The cross-sectional area of the laser beam can be circular in shape.
The method can comprise passing the laser beam through a generally rotationally symmetrical aperture.
The generally rotationally symmetrical aperture can be defined by an iris diaphragm imaged at a distance removed from the corneal region so as to form an out-of-focus image of the iris on the corneal region.
Instead, the generally rotationally symmetrical aperture can be defined by an iris diaphragm imaged on the corneal region, the method including rotating the imaged iris diaphragm.
The laser beam can comprise a series of pulses at a given location, the method comprising angularly displacing the iris diaphragm between the laser beam pulses.
The cross-sectional area of the resultant laser beam can correspond with an area of an epithelial layer extending across an entire surgical site of the eye so as to cause uniform ablation of the epithelial layer across the entire surgical site.
The method can include using the resultant laser beam to uniformly ablate the epithelial layer across the entire surgical site, and then selectively masking portions of the cross-sectional area of the laser beam to sculpt at least part of a stroma surface of the eye to a required shape, after the epithelial layer is uniformly ablated.
According to another aspect of the invention, there is provided a corrective eye surgery system including a laser for generating a laser beam having a cross-sectional area and an energy distribution profile extending across the cross-sectional area; and an optical element disposed in the laser beam and adapting the energy distribution profile of the laser beam to provide a resultant laser beam having a non-uniform resultant energy distribution profile producing a generally uniform ablation depth when the cross-sectional area of the laser beam is directed at a cornea region of a patient""s eye.
The resultant energy distribution can have a centrally disposed higher energy region surrounded by a peripheral lower energy region.
The laser beam can have a generally Gaussian energy distribution profile extending across its cross-sectional area.
The optical element can comprise a diffractive optic through which the laser beam is passed to yield the resultant laser beam.
The cross-sectional area of the resultant laser beam can be circular in shape.
The corrective eye surgery system can further include an arrangement defining a generally rotationally symmetrical aperture.
The corrective eye surgery system can further comprise an imaging system directing an out-of-focus iris image onto the patient""s eye.
The rotationally symmetrical aperture can be defined by an imaged iris, the system further including a drive arrangement associated with the imaged iris for causing angular displacement of the imaged iris about an axis of the laser beam.
The cross-sectional area of the resultant laser beam can correspond to an area of an epithelial layer extending across an entire surgical site of the eye to cause uniform ablation of the epithelial layer across the entire surgical site.
The corrective eye surgery system can further include a masking arrangement for selectively masking portions of the laser beam to sculpt a stroma surface after the epithelial layer has been uniformly ablated.